Generally, a stereospecific polybutylene is a semi-crystal polymer of 1-butene as a monomer, and is a polyolefin having a high molecular weight, and has generic physical properties similar to those of polyethylene or polypropylene.
A stereospecific polybutylene has characteristic features such as high flexural resistance, compatibility with other polymers, rheological properties, crystal behavior and the like. Also, it has a similar density to that of polypropylene and low density polypropylene, and has a similar melting point to that of high density polyethylene. Also, a stereospecific polybutylene has such an excellent stability that it has a long-lasting durability even at a high temperature.
Furthermore, a stereospecific polybutylene has the advantage that it can be readily used in the processes such as extrusion, injection, blow molding and the like, because it can be readily used in the conventional machines for said processes in which polyolefin has been used.
Available temperature range of such a stereospecific polybutylene is approximately −20˜105° C. and a stereospecific polybutylene can be applied to various manufactured goods such as hot or cold water pipe, opening of soft package, polypropylene film, fiber-softening agent or capability-enhancing agent of hot melt adhesives and the like.
A stereospecific polybutylene can be obtained by the process that hydrocarbon is used as a solvent or the process that 1-butene in itself is used as a solvent Currently, due to the problem of separation after preparation and the like, a stereospecific polybutylene has been obtained by the latter process commercially.
Generally, a stereospecific polybutylene is obtained by polymerizing 1-butene in the presence of main catalyst based on organic aluminium compound such as diethylaluminium chloride and titanium trichloride.
According to this process, the stereospecificity of produced polybutylene is not high enough and, therefore, non-stereospecific polybutylene should be removed. Moreover, due to its low activity, this process needs the step of removing catalytic residues that deteriorate physical properties of the polymer.
A stereospecific polybutylene can be obtained by polymerizing 1-butene in the presence of the catalytic system consisting of internal electron donor and titanium supported on magnesium chloride.
However, this process does not have a high catalytic activity compared to that of a highly active conventional process for the preparation of polyethylene or polypropylene and, therefore, this process has the problem that titanium components still resides in the polymer in ppm (weight) level.
EP 187,034 A2 discloses a conventional process for the preparation of a stereospecific polybutylene.
In this process, so as to prepare a high stereospecific polybutylene in the form of particle, a lower hydrocarbon such as normal butane, isobutane, normal pentane, isopentane and cyclopentane as a solvent, a Ziegler-Natta catalyst, an organic aluminium compound, an external electron donor (Lewis base) and 1-butene are used in the process of polymerization at 20˜45° C. This process is intended to solve the problem of conventional processes that the used solvent should be removed from produced polybutylene.
This process has advantages that the step of removing non-stereospecific polybutene-1 is not necessary due to the very high stereospecificity of 80 or more of produced polybutylene and the separation of produced polybutylene from the solvent is easy.
However, since the catalytic activity in this process is low (2,360 g/g-cata 4 h, that is, 590 g/g-cata h), the step of removing catalytic residues that deteriorate physical properties of the polymer is required. Also, the catalytic efficiency of this process is too low for the process to be applied effectively to commercial applications.
U.S. Pat. No. 6,306,996 B1 discloses another conventional process for the preparation of a stereospecific polybutylene.
In this process, polybutylene is obtained by 2-stage polymerization of 1-butene in the presence of main catalyst supported on magnesium chloride, wherein 1-butene in itself is used as a solvent and a monomer; and tributylaluminium (TIBA) is used, and diisopropyl dimethoxy silane (DIPMS) is used as an external electron donor.
According to this process, we can obtain the polybutylene that has satisfactory properties, for example, high stereospecificity, a content of catalytic residues expressed in terms of titanium ppm of 50 or less, a molecular weight distribution (Mw/Mn) of 6 or more. Also, this process shows the catalytic activity based on polybutylene homopolymer of 14,000 g/g-cata. 4 h, that is, 3,500 g/g-cata. h.
However, this process also has much lower catalytic activity than that of a highly active process for the preparation of polyethylene or polypropylene and, therefore, it has a long reaction time, which means the decrease of its productivity.